Jeff, Bill, -- Thank you!
I have not been able to find much coherent and systematic information and presentation on wide field astronomy with a cosmologic structural and evolutionary perspective, and this is a shame, as I often miss the broader context when observing isolated NGC/IC objects out there in the universe. So yes! there IS a need for a book on this topic, but as I have explained previously, -- I don't currently feel I have the time to write it (see: https://www.cloudyni...ield/?p=7719242). I do hope someone like Glenn with a deeper astrophysical background than I will do it! . When I run out of steam exploring the universe (I'm not a youngster anymore...), I may take a break though and collect, structure and post all my observing reports on a web site / blog.
So, thanks once again Glenn, for your great description of the morphology of coronal superbubbles in the context of the ISM. Excellent explanation of the density gradient from hot coronal bubbles to ISM and to cold dark condensing MC. The eternal cycle of stellar birth and death... As you write Glenn: "The ISM makes for a fascinating subject, made all the more interesting when considered in the context of the full cycle of star formation and death." Dang, I wish you'd sit down and write that book now!
Meanwhile , on with :
The Orion Complex, Close up:
It’s closing in on midnight this evening in late November (2019-11-25, 23:30 Loc CEST, UT+1), as I’m out in my suburban backyard for a study of the Orion-Eridanus super-bubble plus some closer-up views of the Orion A and B molecular clouds in the young Ori OB-1d associations E of Alnitak in the Belt and behind the Sword. There are a couple of obstacles though: first there’s a 27dy/90% moon blazing close by in lower Gemini at 40° and less than 15° E of central Orion. And second: the transparency is rather poor (4/7) due to a combination of high humidity (93%) and low temperature (-1°C, with the DewPt at -2°C), which has resulted in a high frosty haze creating a halo around the moon and white contrails, when planes cross through the field of view. This is rather magical and beautiful in fact, and as is often the case with this kind of Autumn weather here in Denmark, the seeing is quite good (8/10), but all-in-all the “celestial light pollution” is reducing the SQM to 18.3 (NELM 5.2) and that is not conductive to my planned study of the faint Ori-Eri super-bubble, or even the “Angel Fish” around the Lambda-Ori OB group.
I therefore decide to concentrate tonight’s observations on the relatively bright MC-complexes in the ORI OB-1d association. I start with a 6.5x in 5.5° FOV overview of the region, spanning the sky from Orion’s Belt down to and including the Sword. I’m using my 60mm f/6 finder scope + a TV 55mm EP with a 6nm Hα filter in front and my 4G NV behind the EP. WOW… What a splendid cosmic panorama (cosmorama?) stretching from the Flame, Dagger and Horsehead at Alnitak (ζ Ori) towards the NE, to the bright M42/M43 nebulae towards the S, surrounded by NGC1981 and the Running Man above, and NGC1980 (the Iota Ori complex) below. A beautiful wide field view of stars, ionized nebulae and DMC, which is where NV really excels!
I now increase the magnification to 28x in 1.5° FOV, using a 13mm EP and a 12nm filter to have a closer look at the young Orion OB-1d molecular clouds; First the Ori A-MC with the M42/M43 nebulae. The view is rather good for NV with a 60mm scope (I think), -- The core of M42 (the Huygens Region with the Trap) is easily burned out of course, but by varying the gain on the NV device and the ISO on the phone app I can study quite a lot of details in the wings and body close to real-time, though not at the same level of detail as using longer exposure live video with stacking (HH objects, proplyds/YSO, outﬂows, bow-shocks etc.).
I close with a study of the Ori B-MC (L1630) east of Alnitak. Now this is quite an interesting view compared to what I’ve been able to see with glass only, -- the Flame (NGC2024), Dagger (IC434) and Horsehead (B33) are all easily seen in a FOV that includes the multiple OB-system σ Ori with the central Σ762- Σ761 components plus several more outlying type-B members (of which I’ve labelled 4 below). The central σ Ori AB-components are hot massive stars of type O9.5V + B0.5V, and they are responsible for ionizing the emission nebula known as "Orion’s Dagger” (IC 434). To the E of IC434 is the B1.5-IV subgiant star HD37903 which is illuminating the bright reflection nebula NGC2023, but this RN of course does not show up in 12nm Hα (I’ve marked the star on the snapshot below anyway). The dense MC of NGC2023 contains a small cluster of Young Stellar Objects (YSO), including proto-stellar HH objects and Pre Main Sequence (PMS) T-Tauri stars. Silhouetted against the bright HII region IC434 (Orion’s Dagger) is the dark cloud of dense gas and dust B33, with an emerging “pillar” known as the Horsehead Nebula. The source of the ionization of IC434 as well as the photo-evaporation of the Horsehead pillar is as mentioned the σ Orionis multiple star system. Finally, E of Alnitak is seen the extensive HII region NGC2024, the Flame Nebula, with a broad N-S dark lane and a heavily obscured embedded cluster with associated HII regions blowing out from the N but still bounded by a sharp ionization front towards the S, and two filamentary bubbles: one E and one W. The Flame cluster contains many YSO (HH objects, accretion discs) and also of course some hot ionizing stars, though the ionization sources of the nebula are too obscured to be identified.
It’s getting late (early rather), so I take some quick photos with my iPhone. The phone is running low on power though (the lithium battery does not like temperatures below zero), so I have to hurry with the Flame/Horsehead snapshot before the phone closes down. I don’t get the gain and ISO settings exactly at its best for this object, so the image is somewhat grainier than was the view, -- but you should be able to see what I’m talking about…
Some final notes on my latest Orion studies:
It has been interesting to see all the Orion OB-associations that I have studied previously coming together in these wide field NV observations,
• from the young (<5 Myr) λ-Orionis group in the N around Meissa (Cr69, in the Angel Fish),
• over the oldest OB1a group (~10 Myr) S of Bellatrix (γ Ori),
• to OB1b (~4½ Myr) around the Belt and OB1c (~4 Myr) forming the Sword with the star clusters NGC 1977/80/81 from σ to ι Orionis.
• Especially conspicuous are of course the very young OB1d (< 2 Myr) subgroups including:
- The Ori-B MC: the stars (NGC2024) in the Flame and Dagger Nebulae E of at Alnitak in the Belt, plus
- The Ori-A MC: the stars in the M42/M43 Nebulae behind the Sword (part of a larger S-shaped OMC filament (Orion Molecular Cloud)
For more context on the Orion OB-associations, see my previous posts higher up in this Rich Field thread:
• Lindblad’s Ring and Gould’s Belt: https://www.cloudyni...ield/?p=7693829 ff.
• Orion Blue Stream: https://www.cloudyni...ield/?p=7740223
• Orion OB-1 association: https://www.cloudyni...ield/?p=7682143
The ages and locations of the various Orion OB-1 subgroups indicate that star formation has propagated through a “sweep-up, compress and trigger” process through the proto-Orion cloud in a sequential manner:
• from 1a S of Bellatrix -> to the 25-Ori and 1b subgroups,
• from 1b (the Belt) subgroup -> to the λ Orionis and 1c subgroups
• through the 1c subgroup (Sword) from the N
via the NGC 1981 and 1955 (“Running Man”) groups
down to the ι Ori group (NGC 1980) in the S.
• finally (in the past few Myr) through the 1d subgroups with:
- the Orion A molecular cloud (M42/M43) behind 1c (the Sword), and
- the Orion B molecular cloud (Flame/Horsehead) E of the Belt at Alnitak.
The cluster around ι Orionis (NGC 1980) in Orion OB-1c is probably the parent of the two run-away stars AU Aur and μ Col that were kicked out of the cluster by the supernova explosion which created Bernard’s Loop, the E wall of the great Orion-Eridanus Super-bubble. For detail studies of the different sections of Orion OB-1, see these posts:
• Lambda Ori (Angelfish): https://www.cloudyni...ield/?p=7689747
• 1a subgroup : https://www.cloudyni...ield/?p=7682150
• 1b subgroup (Belt) : https://www.cloudyni...ield/?p=7683950
• 1c subgroups (Sword) : https://www.cloudyni...ield/?p=7685870
• Sigma Orionis group: https://www.cloudyni...ield/?p=7684634
• 1d subgroup (M42/43): https://www.cloudyni...ield/?p=7685902
• Ori OB-1 Runaway stars: https://www.cloudyni...ield/?p=7687660
Edited by AllanDystrup, 28 November 2018 - 07:57 AM.